Sorry, but nothing from your Brothers house should be getting sent back to the mothers, with the exception of the jacket and shoes they wore from her house to his. You could even send them back in the same clothes, but wash them first (unless of coarse they are only they for a day).
I have custody of my daughter (12yrs old) and she goes to her fathers everyother weekend and one night a week. Of coarse holiday's are split as well. When she was younger I would have to send a bag to his house that included clothes for the time she was there, snowpants, boots, shoes and so on. Well after many pieces of clothing coming back ruined or not even being worn, I brought this up with court person we were working with and decided that I send her on Friday with the clothes she is wearing and she comes back home in the same clothes on Sunday (not washed of coarse).
I assume your brother pays her support and that is to buy things the kids need. He should not be paying support AND sending everything back to her house in order for her to care for the children. It kills me to read this...I can't believe they are required to strip there beds to bring bedding back to her house.
As far as clothes being ruined, what I did is send her in garage sale clothes, or used clothes I didn't care as much about. Go on Craigslist, many people even give stuff away for free.
So I would say, get used, or cheap jackets, shoes and clothing to send with the kids to her house and keep the good stuff with your brother. Also DO NOT let them bring personal belongings to her house you don't want ruined or even left at her house. DON'T buy Gift Certificates, unless you brother will be the one spending them NOT her.
Feel free to message me if you have any other questions.....